Synthetic textile materials, such as nylon and polyester, are uncomfortable to wear due to their poor permeability to water. In hot weather, sweat cannot easily penetrate (or wick) through these fabrics and evaporate. The poor wicking and permeability are due to the natural hydrophobicity of nylon and polyester polymers; water does not readily spread out over surfaces composed of these materials. Nylon and polyester also often exhibit static cling and stain retention due to their hydrophobicity.
A method for imparting durable hydrophilic properties to nylon, polyester, and other synthetic materials would thus be desirable. This may be achieved by attaching hydrophilic materials to the hydrophobic fibers. Imparting hydrophilic properties to the hydrophobic substrate will also diminish or eliminate static cling and enable the release of stains during laundering.
U.S. Pat. No. 3,377,249 to Marco discloses the application of a stain-releasing finish to fabrics made of polyester, cotton, and polyester/cotton blends. The formulations comprise an acrylate copolymer (composed of at least 20% acrylic acid monomer) emulsion, an aminoplast resin, and a resin catalyst. The fabrics thus treated show stain-releasing properties durable to between five and ten home launderings.
Michielsen and Tobiesen have reported a method of grafting poly(acrylic acid) (or PAA) onto nylon 6,6 films (Tobiesen, F. A., Michielsen, S.; J. Poly. Sci. A; 40, 719-728 (2002)). In this method, nylon 6,6 films were dipped in aqueous solutions containing PAA, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS). It is reported that the carboxylates of the PAA are activated by reaction with EDC; some of the activated carboxylates then react with amine groups on the chain ends of the nylon polymers while the rest are hydrolyzed back to carboxylate form. The NHS is believed to aid in slowing the rate of hydrolysis. After incubating the film in the solutions for times ranging from 0.5 to 18 hours, and at temperatures ranging from 0 to 60° C., the treated films were removed and rinsed at least six times with deionized water. The authors report that a drop of water placed on untreated nylon 6,6 film spreads slowly over the surface, whereas a drop placed on a treated film immediately spreads to cover the surface. Disadvantages to this method are that large amounts of the expensive reagents EDC and NHS, in greater-than-stoichiometric amounts relative to the number of carboxyl groups, are required for grafting.
Herein is disclosed the invention of a treatment for polyester, nylon, and other synthetic, hydrophobic materials that renders the treated material hydrophilic. The treatment durably attaches hydrophilic material directly to a hydrophobic substrate, rendering the substrate hydrophilic without altering the other properties of the material.